The invention relates to modifying the rigid substrate of a fixed abrasive article used in semiconductor wafer modification.
Chemical mechanical planarization (CMP) processes are used in semiconductor wafer fabrication to polish and planarize a semiconductor wafer. CMP processes involve placing an abrasive between a relatively stiff pad and a semiconductor wafer and moving the pad and the semiconductor wafer in relation to each other to modify the surface of the wafer. The abrasive used in a CMP process can be in the form of a slurry, i.e., a liquid medium that includes abrasive particles, or a fixed abrasive element, e.g., an element that includes abrasive particles bonded to a backing.
CMP processes attempt to remove material selectively from relatively higher locations, i.e., features having dimensions on the scale of those features commonly produced by photolithography, to planarize the wafer surface. CMP processes also attempt to remove material uniformly on the scale of the semiconductor wafer so that each die on the wafer is planarized to the same degree in an equivalent period of time. The rate of planarization for each die is preferably uniform over the entire wafer. It is difficult to achieve both of these objectives simultaneously because semiconductor wafers are often warped or curved. Some semiconductor wafers also include numerous step height variations or protrusions, which are produced during the fabrication sequence of an integrated circuit on a wafer. These height variations and the curvature and warp of the semiconductor wafer can interfere with the uniformity of the polishing process such that some regions of the wafer become over polished while other regions remain under polished.
CMP processes that employ a slurry have been modified in an effort to overcome the problem of non-uniform polishing. One such effort employs a composite polishing pad that includes a first layer of elastic material, which is attached to a polishing table, and a second layer of a stiff material covering the elastic layer. The second layer includes an array of tiles separated by channel regions. The channel regions channel slurry across the surface of the polishing pad during the polishing process. Other composite polishing pads include a third layer of a relatively low modulus spongy porous material that transports slurry across the surface of the wafer being polished. During polishing liquid can be transported through the porous material and into the lower layers of the polishing pad.
Fixed abrasive CMP processes do not rely on the transport of loose abrasive particles over the surface of the polishing pad to effect polishing. Instead, such processes use fixed abrasive polishing pads, which include a number of three-dimensional abrasive composites fixed in location on a backing. The three-dimensional abrasive composites include abrasive particles disposed in a binder and bonded to the backing, which forms a relatively high modulus fixed abrasive element. During the CMP process, the wafer surface is polished by contact with the fixed abrasive composites and a substantial majority of the abrasive particles in the abrasive composites remain bonded to the backing.
After a CMP polishing process the semiconductor wafer will have an edge exclusion zone, i.e., a zone at the edge of a polished semiconductor wafer that is not polished sufficiently to provide useful components, e.g., semiconductor components. The portion of the semiconductor wafer that constitutes the edge exclusion zone could be used to make semiconductor devices if it were uniform. Thus, the area of the edge exclusion zone affects the die yield of the wafer.